Placenta Growth Factor (PLGF) was recently identified as a novel therapeutic target for inhibiting tumor angiogenesis. PLGF is a member of the vascular endothelial growth factor (VEGF) family, which binds to and signals through the VEGF-R1 receptor. Tumor cells produce PLGF and VEGF in response to hypoxic conditions caused by chemotherapy, radiation or VEGF inhibition therapy. In tumors, hypoxia inducing factor HIF11 can upregulate PLGF and VEGF, which then enter the periphery, bind to and recruit endothelial cells, thus initiating neovascularization. While VEGF has an essential role in normal vascularization and development, PLGF does not. Normally, PLGF has a limited pattern of expression, but it is unexpectedly produced by different tumors. Therefore, inhibiting PLGF as a cancer treatment would be more selective, and is predicted to be less toxic than inhibiting VEGF. Furthermore, PLGF inhibition is predicted to enhance anti- angiogenic therapy with VEGF inhibitors, by blocking PLGF's ability to recruit macrophages. Macrophage recruitment to the tumor microenvironment has been associated with tumor resistance. In addition, mouse tumor model studies indicated that anti-PLGF neutralizing antibodies inhibited growth, angiogenesis and macrophage recruitment in a variety of tumors, suggesting that PLGF inhibition might be effective against human cancers. Recently, gene expression microarray studies have identified PLGF transcripts in a variety of head and neck squamous cell carcinomas (HNSCC), suggesting that PLGF inhibition might have therapeutic benefit in HNSCC. In this pilot study, we aim to investigate the role of PLGF in HNSCC, characterizing the activity of newly isolated human monoclonal antibodies (Hu MAbs) specific for PLGF. We hypothesize that PLGF inhibition will have anti-tumor activity in HNSCC, and will inhibit tumor angiogenesis and macrophage recruitment both in vitro and in vivo. PLGF specific Hu MAbs have recently been isolated in our laboratory using a novel in vitro technology. We propose in aim 1 to identify a role for PLGF in HNSCC in vitro, staining HNSCC specimens for PLGF prior to and after hypoxia induction through chemoradiation. In addition, we will compare antibody inhibition and siRNA knockdown of PLGF production in HNSCC cell lines and tumor specimens, looking at effects on VEGF-R1 binding, MAP kinase activity, angiogenesis induction and monocyte recruitment. We propose in aim 2 to identify a role for PLGF in HNSCC in vivo, using a xenograft animal model of tumor angiogenesis. Immunodeficient mice will be injected with human HNSCC cell lines expressing high, low, or knocked down levels of PLGF, in the presence or absence of PLGF Hu MAbs. Effects on tumor growth, neovascularization, and human leukocyte and macrophage recruitment will be evaluated. In summary, the goal of this pilot project proposal is to investigate the role of PLGF in HNSCC. It is expected that the proposed studies will provide the rationale for further exploration of this exciting new angiogenic target in head and neck cancer. PUBLIC HEALTH RELEVANCE: In this proposal, we aim to investigate the role of Placenta Growth Factor (PLGF), a member of the VEGF family, in head and neck squamous cell carcinoma (HNSCC). PLGF normally has limited expression, but is aberrantly expressed in tumors, causing angiogenesis and macrophage recruitment. Novel PLGF specific human monoclonal antibodies will be tested for in vitro and in vivo anti-tumor activity on HNSCC. The goal of this proposal is to investigate their activity for use as possible immunotherapeutic agents in HNSCC.